An unusual clinical presentation of a plunging ranula—The plunging ranula with extension to the vallecula

Key Clinical Message A plunging ranula may present initially as an extensive vallecular cyst and correct diagnosis may be reached with the use of ultrasound, fluid aspiration for amylase detection, and MRI imaging. Abstract The ranula is a pseudocyst of the sublingual salivary gland and can be divided into two known subtypes. The simple ranula and plunging ranula. While the simple type can be found in the floor of the mouth, the plunging ranula usually pervades the mylohoid muscle and presents as a cervical swelling. The presented case should outline the difficulties in diagnostic and treatment of an uncommon expression of a mucocele above the mylohoid muscle without presenting either a cervical or an intraoral swelling, only extending towards the vallecula. We present a previously unreported clinical manifestation of a ranula of an 18‐year old male, which extends posteriorly, remaining confined in the supramylohyoid muscle space. The cystic lesion protrudes in the oropharynx, and clinically appears as an extensive vallecular cyst. On magnetic resonance imaging the initial suspected diagnosis of a vallecular cyst was changed to the final diagnosis of a plunging ranula. The marsupialization of the cyst sac was performed. Outpatient follow‐up revealed a persisting ostium, indicating a continuous extravasation of the sublingual gland. The present case report describes an unusual clinical presentation of a plunging ranula, remaining above the mylohyoid muscle and protruding into the oropharynx, misdirecting to the first suspected diagnosis of a vallecular cyst. The case highlights the useful contribution of the MRI imaging for differential diagnoses and the need for criteria to indicate further investigations.


| BACKGROUND
The ranula is an extravasation cyst of the sublingual gland that is usually caused by trauma with a consecutive tearing of the duct of Rivinus. 1,2][5] The clinical presentation can be divided into two types.The intraoral or simple ranula usually presents as a livid, cystic mass on the floor of the oral cavity, lateral to the lingual frenulum and confined to the supramylohyoid space. 6It leads to dysphagia or throat lump, 7 usually appears unilateral, and children and young adults seem to be more affected. 8he plunging ranula is a mucocele 9 with an hourglassshaped herniation through the mylohyoid muscle into the submandibular region, mainly due to a defect in the corresponding muscle, presenting as cervical swelling. 6,10,11ccasionally, it leaves the sublingual region via the posterior margin of the mylohyoid rather than through a mylohyoid hiatus. 12In addition to injury to the glandular excretory duct, a genetic predisposition has been suggested. 13The plunging ranula may or may not have an oral component. 3ince spontaneous remission is rarely observed, current literature agrees on the performance of a treatment.5][16] For the simple intraoral ranula, marsupialization provides a less invasive technique and is therefore still frequently used. 2,4,7,179][20] The literature rather suggests the avoidance of the excision of the ranula itself. 2,21,224][25] However, an open surgical intervention is still related to potential complication, such as the damage of surrounding tissue like the lingual nerve or the wharton's duct. 26n this case report, we aim to present a rare variant of expansion of the ranula and report difficulties in diagnostics and treatment of this uncommon manifestation.

| CASE REPORT
An 18-year-old male patient with a body mass index (BMI) of 37.4 presented with a 2 week history of progressive dysphagia and pharyngeal globus sensations.He reported difficulty in breathing, especially in the supine position, and intermittent dysphonia.Oral food intake was unrestricted.The patient reported no previous diseases, was not taking medication on a regular basis, and had no known allergies.

| Investigations
ENT examination revealed a just slightly swollen floor of the oral cavity with prominent plicae (Figure 1).Flexible transnasal endoscopy revealed an extensive cystic, smooth-edged mass in the vallecula on the right side, extending to the epiglottis and partially displacing it (Figure 2).The endolarynx could only be examined using flexible endoscopy during phonation and had regular presentation.No masses or lymphadenopathy were palpable in the neck.An expansive vallecular cyst was suspected based on the clinical presentation.As the patient had progressive symptoms and an elevated white blood cell count, direct ward admission was indicated with panendoscopy and removal of the presumably infected cyst the following day.The leucocytes were elevated to 12.4 Bn/L and the C-reactive protein (CRP) level was 8 mg/L.No fever was present.
Intraoperatively, the cystic sac was located above the right hypopharynx and vallecular.These structures were concealed by it and thus could not be adequately assessed.In order to get a better picture of the expression, the decision to perform intraoperative ultrasound diagnostic was made.Following ultrasonography in the theater brought up the suspected diagnoses of a plunging ranula, a herniated median thyroglossal duct cyst or external laryngocele to level IB.The planned excision was not performed and the procedure was terminated for further investigations.
Following magnetic resonance imaging 27 of the neck with contrast enhancement showed a large ranula of the right sublingual gland above the mylohyoid muscle, without contact to the submandibular gland, sliding into the ipsilateral vallecula, and with a maximum extent of 7.6 × 2.8 cm (Figures 3 and 4).

| Treatment
Due to its extension throughout the whole base of the tongue and the patients wish for a minimally invasive procedure, we decided to perform a marsipialization.This was carried out under general anesthesia.Using a C-shaped cheek retractor and a Denhart mouth gag, Wharton's duct on the right side was initially dilated.Probing the duct with a myrtle leaf probe was only possible up to approximately 1 cm because of stenosis.After mucosal incision, the cystic sac was carefully dissected bluntly.The lingual nerve was identified, dissected, and entwined with a vessel loop (Figure 5).The anterior part of the cyst was mobilized from the surrounding tissue, resulting in accidental opening and discharge of viscous secretions without pus.Marsupialization of the cyst sac and suturing of the wound edges with 4-0 Vicryl stitches were performed, creating a large ostium of about 1 cm (Figure 6).Examination of the base of the tongue at the end of surgery showed complete regression of the mass.
The histologically processed tissue showed findings that were clearly indicative of an extravasation mucocele of the sublingual gland with a nonepithelial lining of the cavity (Figures 7 and 8).There was mild active inflammation of the adjacent parenchyma and no evidence of malignancy.
In an outpatient follow-up 6 month after surgery a shrinkage of the ostium and low progression of the vallecular protrusion was observed.Considering the patients will, we once more decided to surgically enlarge the ostium.Outpatient follow-up after 8 months revealed no evidence of recurrence of the ranula itself but a still persisting ostium.
F I G U R E 3 T2-weighted contrast-enhanced MRI of the neck (right paramedian sagittal section) showing a contrast-absorbing mass extending posteriorly cranial to the mylohyoid muscle, reaching beyond the base of the tongue into the vallecula.

| DISCUSSION
The morphology of the ranula described in our case with posterior extension of the cyst above the mylohyoid muscle posteriorly into the vallecula has not been previously reported.There only have been isolated reports of parapharyngeal extension of the formation from the supraclavicular region to the base of skull. 10,28-31However, since a plunging ranula is commonly defined as a mucocele passing through the mylohyoid muscle and causing a cervical swelling, we suggest the usage of the term plunging ranula with extension to the vallecula.It is an unusual clinical presentation with differing differential diagnoses to be considered than for common plunging ranulas.
The reason for this unusual expression can only be conjectured.First, there could be an embryonic disposition or stenosis 32 supporting a slow development of the ranula over years and an exacerbation in size due to an infection.This would further explain the rapid progression of symptoms and the increased amount of white blood cells.Alternatively, an unremembered trauma of the sublingual gland could be causative for the extravasation. 3,33As the mylohyoid muscle can be stated to be intact and without predilection site for herniation, 10,31 a deviation to the oropharyngeal region seemed to be the weakest point for extension.
As this manifestation of a ranula is new, the initial suspected diagnosis made by transnasal flexible endoscopy led to an incorrect assumption of a vallecular cyst.Following ultrasound diagnosis also failed to show a holistic picture of the expression but pointed out a large cystic formation at the floor of the mouth, which led to the decision for further investigations.For this reason, ultrasound diagnostic seems to be an effective and fast tool for the diagnosis of a plunging ranula with a cervical swelling and can pave the way for further treatment decisions. 34In our case, only MRI imaging was able to fully demonstrate the expansion of the cyst and was necessary for final diagnosis and treatment decision.
While preoperative imaging with ultrasound or MRI appears reasonable in the presence of a plunging ranula with a cervical component to differentiate it from other suspected diagnoses such as a lymph node enlargement, an epidermoid cyst, a lateral neck cyst, a herniated thyroglossal cyst, a cystic hygroma, or an external laryngocele, 3,11,16,33,35 the absence of a visible cervical swelling makes differential diagnoses more difficult.However, if a massively extended vallecular cyst is present, further imaging may be useful.Therefore, it is important to differentiate patients who need further investigations from those who do not, as most patients with a suggested vallecular cyst will not have a rare manifestation of a plunging ranula.Criteria for further investigations prior to intervention may be a rapid progression of symptoms, young age, and a flexible-endoscopically visualizable cyst that already obscures neighboring structures.Ultrasound diagnostics, fluid aspiration for amylase detection 11,36 and MRI imaging may then be critically evaluated before intervention.
Extirpation of the sublingual gland without the ranula is stated to be treatment of choice, 2,26,37,38 but the present patient urgently expressed the wish for the most minimally invasive therapy.We therefore decided to marsupialize the  ranula.Nevertheless, this case report highlights that extensive marsupialization alone may result in a persistent ostium, only allowing longterm drainage without leading to sufficient fibrosis and healing.This does not only cause complaints but might potentially lead to recurrence in the long term.For this reason, marsupialization alone is not a sufficient therapeutic option and the result of our outpatient follow-up indicates that the removal of the associated sublingual gland is necessary for cure. 21

| CONCLUSION
Diagnosis and therapy of this unusual manifestation of a plunging ranula with extension to the vallecula, initially presenting as a symptomatic vallecular cyst, is difficult and challenging.Even though in most cases ultrasound diagnostic is perfectly adequate, in this case, MRI imaging, was instrumental to lead to the right diagnosis.The report underlines the importance of preoperative considerations of rare diagnoses and consequences for treatment.

F I G U R E 1
Preoperative intraoral examination showing a minimally enlarged caruncula.F I G U R E 2 Preoperative flexible transnasal endoscopy showing a mass resembling a vallecular cyst.

F
I G U R E 4 T2-weighted contrast-enhanced MRI of the neck (transverse section at the level of the contrast agent) showing a plunging ranula almost completely filling the floor of the oral cavity.F I G U R E 5 Intraoperative identification of the right sublingual nerve (entwined with a vessel loop).F I G U R E 6 Transoral view.The final result after marsupialization of the plunging ranula, creating a large ostium allowing sufficient drainage.

F I G U R E 7
Overview image of the extirpated tissue with hematoxylin-eosin (HE) staining showing normal squamous epithelium on the surface (SE; top), sparse residual salivary gland tissue (SGT; lower left), and ranula (R; cystic structures in the center of the specimen).

F I G U R E 8
Enlarged section of the extravasation mucocele with HE-staining.The wall shows chronic granulating inflammation.There is no epithelial lining.In the lower left corner of the image, remnants of the local squamous epithelium (SE) are still visible for orientation.